Light-emitting device

ABSTRACT

A light-emitting device is provided, which includes a package having a first portion and a second portion surrounding it, a semiconductor light-emitting element mounted on the first portion and emitting a light having an emission peak in a near-ultraviolet region, a transparent resin layer covering the semiconductor light-emitting element and contacted with the package, and a laminated body formed on the transparent resin layer with end faces of the laminated body being contacted with the second portion. The transparent resin layer has an arch-like outer profile perpendicular cross section. The laminated body has an arch-like outer profile in perpendicular cross section and comprises a red fluorescent layer, a yellow fluorescent layer, a green fluorescent layer and a blue fluorescent layer laminated in the mentioned order. The yellow fluorescent layer has a top portion which is made larger in thickness than that of the end face portions thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-225887, filed Aug. 31, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a light-emitting diode (hereinafter referredto as LED) and a light-emitting device employing a semiconductorlight-emitting element such as a semiconductor laser diode (hereinafterreferred to as LD).

2. Description of the Related Art

In recent years, much attention has been paid to so-called white LEDs,where white light is emitted using a single chip comprising acombination of a blue LED employed as an excitation light source and ayellow fluorescent substance such as YAG:Ce. Although this white LED issimple in construction, the white color to be emitted therefrom is poorin a red component. Because of this, the white light obtained from acombination consisting of only the blue emission to be derived from anexcitation light source and the yellow fluorescent substance has beenrealized as being defective in that it lacks in color rendering.Therefore, this white light is accompanied with a problem that it isdifficult to apply it for ordinary illumination or as a backlight for aliquid crystal display where high color rendering is demanded.

This problem may be overcome by the co-use of a red fluorescentsubstance. For example, it is possible to obtain an emission color whichis excellent in color reproducibility using a combination of a greenfluorescent substance and a red fluorescent substance with a blue LED.As the green fluorescent substance, it is possible to employ (Sr, Ca,Ba) (Al, Ga)₂S₄:Eu, BaMgAl₁₀O₁₇:Eu, etc. As the red fluorescentsubstance, it is possible to employ (Ca, Sr) S:Eu, CaLa₂S₄:Ce, etc.

There is also proposed a light-emitting device in JP-A 2000-509912(KOHYO) wherein a blue fluorescent substance, a green fluorescentsubstance and a red fluorescent substance are used in combination withan ultraviolet LED. Since the color of emission to be obtained dependsonly on the mixing ratio of fluorescent substances, the preparation ofthe light-emitting device would appear to be simple. Therefore, as faras the color rendering is concerned, this light-emitting device is moreexcellent than the light-emitting device to be obtained from a blue LEDwhich is combined with only a yellow fluorescent substance.

When several kinds of fluorescent substances are employed, there is thepossibility that fluorescence may be re-absorbed. There is also proposeda light-emitting device in JP-A 2005-277127 (KOKAI) wherein a pluralityof fluorescent substances each differing in fluorescent wavelengthemitted are disposed along the route of light to be emitted externallyfrom an excitation element in such an order that the fluorescentsubstance exhibiting a longer fluorescent wavelength is arranged moreclose to the excitation element, thereby suppressing the re-absorptionof fluorescence. Specifically, a layer of fluorescent substance emittinga long wavelength (a wavelength closer to red color) is disposed in thevicinity of the excitation element and a layer of fluorescent substanceemitting a short wavelength (a wavelength closer to blue color) isdisposed at an outer position located away from the excitation element,thereby suppressing the re-absorption of fluorescence and enhancing thebrightness of the light.

BRIEF SUMMARY OF THE INVENTION

A light-emitting device according to one aspect of the present inventioncomprises:

a package having, on a surface thereof, a first portion and a secondportion surrounding the first portion;

a semiconductor light-emitting element mounted on the first portion andemitting a light having an emission peak at a near-ultraviolet region;

a transparent resin layer covering the semiconductor light-emittingelement and contacted with the first portion and the second portion, thetransparent resin layer having an arch-like outer profile, as seen in across section when cut perpendicularly to the surface; and

a laminated body formed on the transparent resin layer with end faces ofthe laminated body being contacted with the second portion, thelaminated body having an arch-like outer profile, as seen in a crosssection when cut perpendicularly to the surface and comprising a redfluorescent layer, a yellow fluorescent layer, a green fluorescent layerand a blue fluorescent layer which are laminated in the mentioned order,the yellow fluorescent layer having a top portion larger in thicknessthan that of the end face portions thereof.

A light-emitting device according to another aspect of the presentinvention comprises:

a package having, on a surface thereof, a first portion and a secondportion surrounding the first portion;

a semiconductor light-emitting element mounted on the first portion andemitting a light having an emission peak at a near-ultraviolet region;

a first transparent resin layer covering the semiconductorlight-emitting element and contacted with the first portion and thesecond portion, the first transparent resin layer having an arch-likeouter profile, as seen in a cross section when cut perpendicularly tothe surface; and

a laminated body formed on the first transparent resin layer with endfaces of the laminated body being contacted with the second portion, thelaminated body having an arch-like outer profile, as seen in a crosssection when cut perpendicularly to the surface and comprising a redfluorescent layer, a yellow fluorescent layer, a second transparentresin layer, a green fluorescent layer and a blue fluorescent layerwhich are laminated in the mentioned order, the second transparent resinlayer having a top portion larger in thickness than that of the end faceportions thereof.

A light-emitting device according to a further aspect of the presentinvention comprises:

a package having, on a surface thereof, a first portion and a secondportion surrounding the first portion;

a semiconductor light-emitting element mounted on the first portion andemitting a light having an emission peak at a blue color region;

a transparent resin layer covering the semiconductor light-emittingelement and contacted with the first portion and the second portion, thetransparent resin layer having an arch-like outer profile, as seen in across section when cut perpendicularly to the surface; and

a laminated body formed on the transparent resin layer with end faces ofthe laminated body being contacted with the second portion, thelaminated body having an arch-like outer profile, as seen in a crosssection when cut perpendicularly to the surface and comprising a redfluorescent layer, a yellow fluorescent layer and a green fluorescentlayer which are laminated in the mentioned order, the yellow fluorescentlayer having a top portion made larger in thickness than that of the endface portions thereof.

A light-emitting device according to a further aspect of the presentinvention comprises:

a package having, on a surface thereof, a first portion and a secondportion surrounding the first portion;

a semiconductor light-emitting element mounted on the first portion andemitting a light having an emission peak at a blue color region;

a first transparent resin layer covering the semiconductorlight-emitting element and contacted with the first portion and thesecond portion, the first transparent resin layer having an arch-likeouter profile, as seen in a cross section when cut perpendicularly tothe surface; and

a laminated body formed on the first transparent resin layer with endfaces of the laminated body being contacted with the second portion, thelaminated body having an arch-like outer profile, as seen in a crosssection when cut perpendicularly to the surface and comprising a redfluorescent layer, a yellow fluorescent layer, a second transparentresin layer and a green fluorescent layer which are laminated in thementioned order, the second transparent resin layer having a top portionmade larger in thickness than that of the end face portions thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a graph showing the excitation spectrums and emissionspectrums of fluorescent substances;

FIG. 2 is a cross-sectional view of a light-emitting device according toone embodiment;

FIG. 3 is a cross-sectional view of a light-emitting device according toanother embodiment;

FIG. 4 is a cross-sectional view of a light-emitting device according toa further embodiment;

FIG. 5 is a cross-sectional view of a light-emitting device according toa further embodiment;

FIG. 6 is a cross-sectional view of a light-emitting device of onecomparative example;

FIG. 7 is a cross-sectional view of a light-emitting device of anothercomparative example;

FIG. 8 is a cross-sectional view of a light-emitting device of a furthercomparative example;

FIG. 9 is a cross-sectional view of a light-emitting device of a furthercomparative example;

FIG. 10 is a cross-sectional view of a light-emitting device of afurther comparative example; and

FIG. 11 is a cross-sectional view of a light-emitting device of afurther comparative example.

DETAILED DESCRIPTION OF THE INVENTION

Next, embodiments will be explained in detail with reference to thedrawings.

The present inventors have found out the following facts with respect tothe excitation/emission spectrums of a plurality of fluorescentsubstances. These findings will be explained with reference to FIG. 1.FIG. 1 shows the excitation/emission spectrums of CaAlSiN₃:Eu(hereinafter referred to simply as CASN), BaMgAl₁₀O₁₇:Eu (hereinafterreferred to simply as BAM), (Ba,Ca,Mg)₁₀(PO₄)₆.Cl₂:Eu (hereinafterreferred to simply as BCA) and (Sr,Ca,Ba)₂SiO₄:Eu (hereinafter referredto simply as SOSE).

CASN absorbs the light ranging from near-ultraviolet to blue light andemitting red light. BAM or SCA absorbs an ultraviolet ray and emittingblue fluorescence. The present inventors have found out that when CASNis present in the vicinity of a fluorescent substance emitting bluelight, the blue emission is absorbed by the CASN. This is a phenomenonthat occurs due to the overlapping of the absorption band of one of thefluorescent substances with the fluorescent band of the other.

Therefore, when a fluorescent layer comprising a mixture consisting ofplural kinds of fluorescent substances is employed in combination withan excitation light source, the aforementioned re-absorption offluorescence generates, thereby decreasing the quantity of light to beultimately released out of the light-emitting device. This phenomenon ofre-absorption occurs without depending on the excitation light source.For example, even when an ultraviolet LED chip emitting light having awavelength ranging from 375 to 420 nm or a blue color LED chip emittinglight having a wavelength ranging from 430 to 480 nm is employed as alight source, this phenomenon of re-absorption occurs. Even if thecontent of fluorescent substances is increased in an attempt to obtain awhite light source of high efficiency, the aforementioned re-absorptionleads to only the increase of red color emission, thus resulting in thedeterioration of white color luminance. This re-absorption offluorescence would occur not only in the case of CASN but also in thecase of any kind of fluorescent substance as long as it has anabsorption band falling within the visible light zone.

It is considered possible to suppress the aforementioned re-absorptionby arranging a plurality of fluorescent substances each differing inemitting fluorescent wavelength along the route of light to be emittedexternally from an excitation element in such an order that thefluorescent substance exhibiting a longer fluorescent wavelength isarranged more close to the excitation element. Specifically, afluorescent substance emitting a long wavelength (a wavelength closer tored color) is disposed in the vicinity of the excitation element and alayer of fluorescent substance emitting a short wavelength (a wavelengthcloser to blue color) is disposed at an outer position located away fromthe excitation element. However, it has been found out by the presentinventors that when fluorescent substances are arranged in such a manneras mentioned above, not only the emission efficiency thereof wouldbecome insufficient but also the conversion efficiency would becomeextremely deteriorated as compared with ordinary fluorescent lamps. As aresult of the extensive studies made by the present inventors in anattempt to further enhance the emission efficiency, the presentinvention has been accomplished wherein a specific fluorescent layer ofa light-emitting device is formed so as to create a distribution inthickness.

In the light-emitting device shown in FIG. 2, a semiconductorlight-emitting element 3 acting as an excitation light source isdisposed at a first portion of a package portion 1 made of an inorganicor organic material and provided with a reflection film (not shown)which is made of Ag, etc. A resin layer, to be explained hereinafter, isdisposed at a second portion which is formed to surround the firstportion of package portion (package) 1. The p-type electrode (not shown)of the semiconductor light-emitting element 3 is electrically connected,via a wire 4, with a lead-out electrode 2 a of anode side. The n-typeelectrode (not shown) of the semiconductor light-emitting element 3 iselectrically connected, via a paste (not shown), with a lead-outelectrode 2 b of cathode side. Incidentally, the lead-out electrode 2 aof the anode side and the lead-out electrode 2 b of the cathode side areboth employed for mounting this light-emitting device on a wiringcircuit board, etc.

On the semiconductor light-emitting element 3 is disposed a transparentresin layer 5 having an arch-like outer profile. The end faces of thistransparent resin layer 5 are contacted with the second portion ofpackage portion 1. As the material of this transparent resin, it ispossible to employ silicone resin, for example. Further, as specificfeatures of the arch-like curve, it may be selected from any optionalcurve such as semi-circular arc, parabolic curve, etc. By interposingthe transparent resin layer 5 between the semiconductor light-emittingelement and the fluorescent layer, it becomes possible to enhance theemission output of the light-emitting device. The fluorescent layer tobe laminated on the transparent resin layer 5 can be suitably selecteddepending on the emission peak wavelength of the semiconductorlight-emitting element 3. For example, in the case of the semiconductorlight-emitting element having an emission peak at the near-ultravioletregion, a red fluorescent layer 6, a yellow fluorescent layer 7, a greenfluorescent layer 8 and a blue fluorescent layer 9 are successivelylaminated on the transparent resin layer 5. Each of these fluorescentlayers is also disposed so as to enable the end faces thereof to contactwith the second portion of package portion 1.

Herein, the near-ultraviolet region means a wavelength region of 375-420nm. Each of these fluorescent layers can be constructed by dispersing afluorescent substance emitting a prescribed color in a binder resin. Asthe binder resin, it is possible to employ any kind of resin as long asthe resin is substantially transparent in a region of nearly the peakwavelength of the excitation element as well as in a region of longerwavelength than that of the first mentioned region. As examples of thebinder resin that can be commonly employed, they include silicone resin,epoxy resin, polydimethyl siloxane derivatives having epoxy group,oxetane resin, acrylic resin, cycloolefin resin, urea resin,fluororesin, polyimide resin, etc.

A red fluorescent layer 6 contains, for example, a CASN fluorescentsubstance, a yellow fluorescent layer 7 contains, for example, an SOSEfluorescent substance, a green fluorescent layer 8 contains, forexample, a BCA green fluorescent substance and a blue fluorescent layer9 contains, for example, a BAM fluorescent substance. Ordinary, the redfluorescent layer emits the light in a wavelength region of 600-780 nm,and the yellow fluorescent layer emits the light in a wavelength regionof 550-590 nm. The green fluorescent layer emits the light in awavelength region of 475-520 nm, and the blue fluorescent layer emitsthe light in a wavelength region of 430-475 nm.

By successively laminating the red fluorescent layer 6, the yellowfluorescent layer 7, the green fluorescent layer 8 and the bluefluorescent layer 9 as described above so as to create a laminated body,it is possible to obtain the following effects. Namely, even the lightthat has been emitted from each of the fluorescent substances but turnedback to the interior of the device without being released out of thedevice can be reflected by an interface between the neighboringfluorescent layers. As a result, the probability of light being emittedfrom the device can be increased, thus making it possible to expectfurther enhanced emission efficiency.

As already explained above, in the case of a mixed fluorescent layercontaining a blue fluorescent substance, a green fluorescent substanceand a red fluorescent substance, the fluorescence from the bluefluorescent substance and the fluorescence from the green fluorescentsubstance are absorbed by the red fluorescent substance. Even if thefluorescent substances are respectively included in each of the layers,the fluorescence from the blue fluorescent layer and from the greenfluorescent layer is re-absorbed by the red fluorescent layer if the redfluorescent layer is disposed on the outer side of the blue fluorescentlayer and the green fluorescent layer. According to this embodiment,this phenomenon can be obviated.

The red fluorescent layer 6, the yellow fluorescent layer 7, the greenfluorescent layer 8 and the blue fluorescent layer 9 are all providedwith end faces contacting with the second portion of the package portion1. Including the transparent resin layer 5 to be disposed on the innerside of the red fluorescent layer 6, the fluorescent layers aregenerally formed so as to have a uniform thickness. Whereas, in the caseof the light-emitting device shown in the drawing, the thickness of theyellow fluorescent layer 7 is not uniform, but made non-uniform in sucha manner that the thickness “a” at the top portion thereof is madelarger than the thickness “b” at the end faces thereof.

The present inventors have taken notice of the directivity ofsemiconductor light-emitting element employed as an excitation lightsource and found out the fact that the light distribution of an LED ishigher in the top portion. When the yellow fluorescent layer to beinterposed between the red fluorescent layer and the green fluorescentlayer is formed so as to make the thickness of top portion larger thanthe other portions, the emission potential of the light source can beeffectively utilized. This phenomenon can be explained as follows.Namely, in addition to the enhancement of efficiency of yellow emission,the re-absorption of green light emission and blue light emission can besuppressed, thereby making it possible to effectively take up the greenemission and the blue emission. These findings were first discovered bythe present inventors.

In this embodiment, the green fluorescent layer 8 is disposed on theouter side of the red fluorescent layer 6, the blue fluorescent layer 9is disposed on the outer side of the green fluorescent layer 8. Further,the yellow fluorescent layer 7 is interposed between the red fluorescentlayer 6 and the green fluorescent layer 8. By arranging thesefluorescent layers in this manner, it is possible to suppress there-absorption of fluorescence and, at the same time, to realize a highemission efficiency. Moreover, the yellow fluorescent layer 7 is formedsuch that the thickness “a” at the top portion thereof is made largerthan the thickness “b” at the end faces thereof. Due to the provision ofsuch a thickness distribution, it is now possible to effectivelysuppress the re-absorption of fluorescence.

Although the effect of suppressing the re-absorption of fluorescence canbe derived by simply enlarging the thickness “a” at the top portion ofthe yellow fluorescent layer relative to the thickness “b” at the endfaces thereof, a more sufficient effect can be derived by setting theratio of thickness (a/b) to not less than 1.5. However, since thestructure where the thickness “a” at the top portion of the yellowfluorescent layer is too large is difficult to manufacture, the upperlimit of the ratio of thickness (a/b) should preferably be confined to 4or so.

The light-emitting device of this embodiment can be manufactured by anyoptional method where fluorescent substances each differing in emittingfluorescent wavelength can be laminated in such an order that thefluorescent substance exhibiting a longer fluorescent wavelength comesmore close to the excitation light source. For example, it is possibleto employ a method using a fluorescent substance-containing resin. Thisfluorescent substance-containing resin can be manufactured by dispersinga specific color fluorescent substance in a binder resin and thisprocedure is repeated for each of different fluorescent substances.

The fluorescent substance-containing resin thus prepared is then coatedby a dispenser while controlling the thickness of the fluorescent layerand dried to obtain a fluorescent layer. This procedure is repeated foreach of the fluorescent layers. The fluorescent substance-containingresin may be coated by vacuum printing. As described above, thefluorescent substance-dispersed resins are respectively prepared andrespectively coated, dried and cured while controlling the thickness oflayer. This procedure is repeated for the preparation of each of thefluorescent layers. By the aforementioned procedure, a light-emittingdevice as shown in FIG. 2 can be manufactured.

When a plurality of fluorescent substances which may bring about there-absorption are present, the fluorescent substances are laminated insuch an order that one exhibiting a longer fluorescent wavelength comesmore close to the excitation light source and a layer having the samethickness distribution as described above is introduced between afluorescent layer which is capable of re-absorbing fluorescence and afluorescent layer which is liable to the re-absorption.

Alternatively, the aforementioned effects can be obtained withoutproviding the yellow fluorescent layer with the aforementioned thicknessdistribution. Specifically, a second transparent resin layer 11 isinterposed between the yellow fluorescent layer 7 and the greenfluorescent layer 8 and, at the same time, the second transparent resinlayer 11 is formed in such a manner that the thickness “e” at the topportion thereof is made larger than the thickness “f” at the end facesthereof as shown in FIG. 3. In the case of the light-emitting deviceshown in FIG. 3, the laminated body is constituted by the redfluorescent layer 6, the yellow fluorescent layer 7, the secondtransparent resin layer 11, the green fluorescent layer 8 and the bluefluorescent layer 9. The second transparent resin layer 11 interposedbetween the yellow fluorescent layer 7 and the green fluorescent layer 8acts to suppress the blue light emission and green light emission frombeing re-absorbed by the red fluorescent substance such as CASN. Sincethe second transparent resin layer 11 is formed to have a thicknessdistribution where the thickness at the top portion thereof is madelarger than the thickness at the end faces thereof, it is now possibleto effectively suppress the re-absorption of fluorescence and to achievea high emission efficiency.

Next, one embodiment where a blue LED chip is employed as asemiconductor light-emitting element 3 functioning as an excitationlight source will be explained with reference to FIG. 4. The light ofblue color region 430-480 nm in wavelength is emitted in general. In thelight-emitting device shown in FIG. 4, a transparent resin layer 5having an arch-like outer profile is disposed on the semiconductorlight-emitting element 3. On this transparent resin layer 5, there aresuccessively laminated the red fluorescent layer 6, the yellowfluorescent layer 7 and the green fluorescent layer 8. Since the yellowfluorescent layer 7 is formed to have a thickness distribution where thethickness “i” at the top portion thereof is made larger than thethickness “j” at the end faces thereof, it is now possible toeffectively suppress the re-absorption of fluorescence and to achieve ahigh emission efficiency.

Alternatively, a second transparent resin layer 11 may be interposedbetween the yellow fluorescent layer 7 and the green fluorescent layer 8without providing the yellow fluorescent layer 7 with the aforementionedthickness distribution as shown in FIG. 5. This second transparent resinlayer 11 is formed in such a manner that the thickness “m” at the topportion thereof is made larger than the thickness “n” at the end facesthereof. As described above, the second transparent resin layer 11interposed between the yellow fluorescent layer 7 and the greenfluorescent layer 8 acts to suppress the green light emission from beingre-absorbed by the red fluorescent substance such as CASN. Since thesecond transparent resin layer 11 is formed to have a thicknessdistribution where the thickness at the top portion thereof is madelarger than the thickness at the end faces thereof, it is now possibleto effectively suppress the re-absorption of fluorescence and to achievea high emission efficiency.

Next, examples will be explained.

EXAMPLE 1

In this example, a light-emitting device constructed as shown in FIG. 2was manufactured.

An ultraviolet LED chip exhibiting an emission peak at a wavelengthranging from 400 to 405 nm and having an InGaN-based compoundsemiconductor as an active layer and suitable p/n electrodes wasprepared as a semiconductor light-emitting element 3. This semiconductorlight-emitting element 3 was then secured to a package portion 1 by anAu—Sn paste. This package portion 1 was provided with lead-outelectrodes 2 a and 2 b and with an aluminum nitride-based substratehaving a wiring portion surrounded by a high reflectance material. Thelead-out electrode 2 a of the anode side was electrically connected withthe p-type electrode of the ultraviolet LED chip by an Au wire 4. Thelead-out electrode 2 b of the cathode side was electrically connectedwith the n-type electrode of the ultraviolet LED chip by Au—Sn paste.

Using a silicone-based transparent resin, a transparent resin layer 5was formed on the semiconductor light-emitting element 3. Specifically,first of all, while heating a substrate at a temperature of 150° C. inan air atmosphere and at atmospheric pressure and using a dispenser, asilicone-based transparent resin was coated on the substrate so as toform a layer of an arch-like configuration where a ratio between thethickness of the top portion thereof and the thickness of each of endface portions was approximately 1:1. Thereafter, the resultant body wasallowed to dry at atmospheric pressure at a temperature of 150° C. for10 to 90 minutes to obtain a transparent resin layer 5.

A CASN red fluorescent substance was dispersed in silicone resinemployed as a binder resin to prepare a red fluorescentsubstance-dispersed resin. The red fluorescent substance employed hereinwas found to exhibit an emission peak at a wavelength of 655 nm. Whileheating the substrate at a temperature of 150° C. in an air atmosphereand at atmospheric pressure and using a dispenser, the red fluorescentsubstance-dispersed resin was coated so as to entirely cover thetransparent resin layer 5 and to form a layer of an arch-likeconfiguration having a uniform thickness. Thereafter, the resultant bodywas allowed to dry at atmospheric pressure at a temperature of 150° C.for 10 to 90 minutes to obtain a red fluorescent layer 6. In this redfluorescent layer 6, a ratio between the thickness of the top portionthereof and the thickness of each of end face portions was approximately1:1.

An SOSE yellow fluorescent substance was dispersed in silicone resin toprepare a yellow fluorescent substance-dispersed resin. The yellowfluorescent substance employed herein was found to exhibit an emissionpeak at a wavelength of 555 nm. While heating the substrate at atemperature of 150° C. in an air atmosphere and at atmospheric pressure,the yellow fluorescent substance-dispersed resin was coated on the redfluorescent layer 6 so as to form a layer of an arch-like configurationwhere the thickness “a” of the top portion thereof was made larger thanthe thickness “b” of each of end faces (i.e. a/b=2). Thereafter, theresultant body was allowed to dry at atmospheric pressure at atemperature of 150° C. for 10 to 90 minutes to obtain a yellowfluorescent layer 7.

A BCA green fluorescent substance exhibiting an emission peak at awavelength of 480 nm was dispersed in silicone resin to prepare a greenfluorescent substance-dispersed resin. A BAM blue fluorescent substanceexhibiting an emission peak at a wavelength of 450 nm was dispersed insilicone resin to prepare a blue fluorescent substance-dispersed resin.While heating the substrate at a temperature of 150° C. and using adispenser, the green fluorescent substance-dispersed resin and the bluefluorescent substance-dispersed resin were successively coated on theyellow fluorescent layer 7 so as to entirely cover the underlyingfluorescent layer and to form layers each having an arch-likeconfiguration having a uniform thickness.

Thereafter, the resultant body was allowed to dry at atmosphericpressure at a temperature of 150° C. for 10 to 90 minutes to cure all ofthese fluorescent layers to obtain a light-emitting device having aconstruction as shown in FIG. 2. In these green fluorescent layer 8 andblue fluorescent layer 9, a ratio between the thickness of the topportion thereof and the thickness of each of end face portions wasapproximately 1:1.

COMPARATIVE EXAMPLE 1

The same kinds of CASN red fluorescent substance, SOSE yellowfluorescent substance, BCA green fluorescent substance and BAM bluefluorescent substance as employed in Example 1 were prepared. Then, allof these four kinds of fluorescent substances were mixed with anddispersed in silicone resin to prepare a mixed fluorescentsubstance-dispersed resin.

A light-emitting device having a construction as shown in FIG. 6 wasprepared in the same manner as described above except that the mixedfluorescent substance-dispersed resin was coated on the transparentresin layer 5 to form a mixed fluorescent layer 10 having an arch-likeconfiguration. Incidentally, in this mixed fluorescent layer 10, a ratiobetween the thickness of the top portion thereof and the thickness ofeach of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 2

The procedures described in Example 1 were repeated in the same mannerexcept that the yellow fluorescent layer 7 was coated uniformly so thatthe ratio between the thickness “c” of the top portion thereof and thethickness “d” of each of end face portions thereof became 1:1 (i.e.c/d=1), thereby manufacturing a light-emitting device having aconstruction as shown in FIG. 7.

The light-emitting devices of Example 1, Comparative Example 1 andComparative Example 2 were investigated with respect to the chromaticitycoordinates of luminescent color. As a result, the chromaticitycoordinates were (0.34, 0.37) in the case of Example 1, (0.36, 0.36) inthe case of Comparative Example 1, and (0.38, 0.38) in the case ofComparative Example 2. Namely, the emission of white light wasrecognized in all of these examples.

However, with respect to the total luminous flux and emissionefficiency, while Example 1 indicated 57 (lm/W) and Ra (colorrendering)=82; Comparative Example 1 indicated 19 (lm/W) and Ra=88. InComparative Example 2, they were 51 (lm/W) and Ra=88.

The light-emitting device of Example 1 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Examples. This improvement of emission efficiency can beattributed to the provision of a specific distribution of thickness inthe yellow fluorescent layer 7 as explained below. In the case of thisexample, the emission intensity distribution (light distribution) of theLED chip employed as a semiconductor light-emitting element was notuniform in all of the directions but was made higher in the directiontoward the top portion thereof and lower in the direction toward the endfaces thereof. Therefore, although the emission intensities of the bluefluorescent substance and the red fluorescent substance can be madehigher in the direction toward the top portion thereof, the quantity ofthe light from these fluorescent substances that will be re-absorbed bythe CASN employed as a red fluorescent substance will be increased. Forthis reason, the luminescent color to be obtained would become highlyreddish white, thus generating color shift.

If it is possible to suppress the re-absorption of blue light emissionand green light emission at the top portion of LED chip, the generationof color shift can be prevented. According to the embodiment, thisproblem has been overcome by providing a structure wherein the yellowfluorescent layer 7, which is scarcely capable of re-absorbing bluelight emission and green light emission, is interposed between the redfluorescent layer 6 and the green fluorescent layer 8 and, at the sametime, the thickness in the direction toward the top portion of yellowfluorescent layer 7 is enlarged. When the top portion of the yellowfluorescent layer 7 is made larger in thickness, the blue light emissionand green light emission moving toward the inner circumferential portioncan be increasingly scattered and absorbed by the yellow fluorescentsubstance and the resin.

As a result, the re-absorption of the light emitted from the bluefluorescent substance and green fluorescent substance by the redfluorescent substance can be suppressed, thus making it possible toobtain blue light emission and green light emission withoutdeteriorating the emission efficiency thereof. When the top portion ofthe yellow fluorescent layer 7 is made larger in thickness, it is alsopossible to enhance the intensity of yellow light emission which is highin visibility, thus making it possible to obtain a white LED which isfree from color shift.

As described above, due to the provision of a thickness distribution inthe yellow fluorescent layer 7, it becomes possible to absorb theexciting light without losing the exciting light, thus making itpossible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

Incidentally, the emission intensity distribution of a semiconductorlaser (LD) light source is much higher in the direction toward the topportion thereof than that of the LED. Therefore, even when the LD isemployed as a semiconductor light-emitting element, it is possible toobtain almost the same effects as described above by enlarging thethickness of the top portion of the yellow fluorescent layer 7.

On the other hand, when the thickness of the top portion of the yellowfluorescent layer 7 is not made larger than the end faces, it would beimpossible to obtain the aforementioned effects. For example, when thethickness of the top portion of yellow fluorescent layer 7 is as thin asthe thickness of each of the end faces thereof, the re-absorption by thered fluorescent substance may be increased, thus making the luminescentcolor become strongly reddish white. Even if the thickness of the topportion of yellow fluorescent layer 7 is increased, when the thicknessof each of the end faces thereof is increased likewise, it would beimpossible to enable the light emission from the light source to reachthe green fluorescent layer 8 and the blue fluorescent layer 9 which arelocated at an outer circumferential portion. Since it is impossible inthis case to obtain sufficient green light emission as well assufficient blue light emission, the luminescent color would become alsostrongly reddish white as described above.

EXAMPLE 2

In this example, a light-emitting device constructed as shown in FIG. 3was manufactured. By repeating the same procedures as described inExample 1, a transparent resin layer 5 and a red fluorescent layer 6were formed on the same kind of semiconductor light-emitting element 3as employed in Example 1.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 552 nm was dispersed in silicone resin to prepare a yellowfluorescent substance-dispersed resin. This yellow fluorescentsubstance-dispersed resin was laminated so as to entirely cover the redfluorescent layer 6 and to form a layer of an arch-like configurationhaving a uniform thickness, thereby forming a yellow fluorescent layer7. Then, a second transparent resin layer 11 was formed on the yellowfluorescent layer 7 in such a manner that the thickness “e” of the topportion thereof was made larger than the thickness “f” of each of endfaces thereof (i.e. e/f=2).

Further, a silicone resin layer containing a BCA green fluorescentsubstance exhibiting an emission peak at 480 nm and a silicone resinlayer containing a BAM blue fluorescent substance exhibiting an emissionpeak at 450 nm were successively laminated so as to cover the secondtransparent resin layer 11, each layer having an arch-like configurationhaving a uniform thickness, thereby forming a green fluorescent layer 8and a blue fluorescent layer 9, respectively, thus obtaining thelight-emitting device constructed as shown in FIG. 3.

COMPARATIVE EXAMPLE 3

The procedures described in Example 2 were repeated in the same mannerexcept that the second transparent resin layer 11 was coated uniformlyso as to create a thickness distribution wherein the ratio between thethickness “g” of the top portion thereof and the thickness “h” of eachof end face portions thereof became g/h=1, thereby manufacturing alight-emitting device having a construction as shown in FIG. 8.

The light-emitting devices of Example 2 and Comparative Example 3 wereinvestigated with respect to the chromaticity coordinates of luminescentcolor. As a result, the chromaticity coordinates were (0.35, 0.38) andRa=87 in the case of Example 2, and (0.38, 0.38) and Ra=88 in the caseof Comparative Example 3. Namely, the emission of white light wasrecognized in all of these examples.

However, with respect to the emission efficiency, while Example 2indicated 53 (lm/W), Comparative Example 3 indicated 51 (lm/W).

The light-emitting device of Example 2 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Example 3. This improvement of emission efficiency can beattributed to the provision of a specific distribution of thickness inthe second transparent resin layer 11 as explained below. Namely, thetransparent resin layer 11 was featured to have a transmittance of about90% and to contain voids. By increasing the thickness of thistransparent resin layer 11, the light emitted toward the innercircumferential portions of the blue fluorescent layer 9 and the greenfluorescent layer 8, both located at an outer circumferential portion,can be increasingly scattered and absorbed.

Namely, the probability of the blue light emission and the green lightemission reaching the red fluorescent layer 6 containing CASN would bedecreased. As a result, the blue light emission as well as the greenlight emission can be prevented from being re-absorbed by the CASNemployed as a red fluorescent substance.

In the same manner as in the case of the yellow fluorescent layer 7, byenlarging the thickness of the top portion of the second transparentresin layer 11 and decreasing the thickness of each of end facesthereof, it becomes possible, in the case of the second transparentresin layer 11 also, to secure the blue emission and the green emissionwithout deteriorating the emission efficiency. As described above, dueto the provision of thickness distribution in the second transparentresin layer 11, it becomes possible to absorb the exciting light withoutlosing the exciting light, thus making it possible to obtain a whitelight source which is high in emission efficiency and almost free fromdiscoloration.

EXAMPLE 3

In this example, a light-emitting device constructed as shown in FIG. 4was manufactured.

A blue LED chip exhibiting an emission peak at a wavelength ranging from450 to 470 nm and having an InGaN-based compound semiconductor as anactive layer and suitable p/n electrodes was prepared as a semiconductorlight-emitting element 3. This semiconductor light-emitting element 3was then secured to a package portion 1 by an Au—Sn paste. This packageportion 1 was provided with lead-out electrodes 2 a and 2 b and with analuminum nitride-based substrate having a wiring portion surrounded by ahigh reflectance material. The lead-out electrode 2 a of the anode sidewas electrically connected with the p-type electrode of the blue LEDchip by an Au wire 4. The lead-out electrode 2 b of the cathode side waselectrically connected with the n-type electrode of the blue LED chip byAu—Sn paste.

Using a silicone-based transparent resin, a transparent resin layer 5was formed on the semiconductor light-emitting element 3. Specifically,first of all, while heating a substrate at a temperature of 150° C. inan air atmosphere and at atmospheric pressure and using a dispenser, asilicone-based transparent resin was coated on the substrate so as toform a layer of an arch-like configuration where a ratio between thethickness of the top portion thereof and the thickness of each of endface portions was approximately 1:1. Thereafter, the resultant body wasallowed to dry at atmospheric pressure at a temperature of 150° C. for10 to 90 minutes to obtain a transparent resin layer 5.

A CASN red fluorescent substance was dispersed in silicone resinemployed as a binder resin to prepare a red fluorescentsubstance-dispersed resin. The red fluorescent substance employed hereinwas found to exhibit an emission peak at a wavelength of 655 nm. Whileheating the substrate at a temperature of 150° C. in an air atmosphereand at atmospheric pressure and using a dispenser, the red fluorescentsubstance-dispersed resin was coated so as to entirely cover thetransparent resin layer 5 and to form a layer of an arch-likeconfiguration having a uniform thickness. Thereafter, the resultant bodywas allowed to dry at atmospheric pressure at a temperature of 150° C.for 10 to 90 minutes to obtain a red fluorescent layer 6. In this redfluorescent layer 6, a ratio between the thickness of the top portionthereof and the thickness of each of end face portions was approximately1:1.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 555 nm was dispersed in silicone resin to prepare a yellowfluorescent substance-dispersed resin. While heating the substrate at atemperature of 150° C. in an air atmosphere and at atmospheric pressure,the yellow fluorescent substance-dispersed resin was coated on the redfluorescent layer 6 so as to form a layer of an arch-like configurationwhere the thickness “i” of the top portion thereof was made larger thanthe thickness “j” of each of end faces (i.e. i/j=1.5). Thereafter, theresultant body was allowed to dry at atmospheric pressure at atemperature of 150° C. for 10 to 90 minutes to obtain a yellowfluorescent layer 7.

A BCA green fluorescent substance exhibiting an emission peak at awavelength of 480 nm was dispersed in silicone resin to prepare a greenfluorescent substance-dispersed resin. While heating the substrate at atemperature of 150° C. and using a dispenser, the green fluorescentsubstance-dispersed resin was coated on the yellow fluorescent layer 7so as to entirely cover the underlying fluorescent layer and to form alayer having an arch-like configuration having a uniform thickness.

Thereafter, the resultant body was allowed to dry at atmosphericpressure at a temperature of 150° C. for 10 to 90 minutes to cure all ofthese fluorescent layers to obtain a light-emitting device having aconstruction as shown in FIG. 4. In this green fluorescent layer 8, aratio between the thickness of the top portion thereof and the thicknessof each of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 4

The same kinds of CASN red fluorescent substance, SOSE yellowfluorescent substance and BCA green fluorescent substance as employed inExample 3 were prepared. Then, all of these three kinds of fluorescentsubstances were mixed with and dispersed in silicone resin to prepare amixed fluorescent substance-dispersed resin.

A light-emitting device having a construction as shown in FIG. 9 wasprepared in the same manner as described above except that the mixedfluorescent substance-dispersed resin was coated on the transparentresin layer 5 to form a mixed fluorescent layer 10 having an arch-likeconfiguration. Incidentally, in this mixed fluorescent layer 10, a ratiobetween the thickness of the top portion thereof and the thickness ofeach of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 5

The procedures described in Example 3 were repeated in the same mannerexcept that the yellow fluorescent layer 7 was coated uniformly so thatthe ratio between the thickness “k” of the top portion thereof and thethickness “l” of each of end face portions thereof became 1:1 (i.e.k/l=1), thereby manufacturing a light-emitting device having aconstruction as shown in FIG. 10.

The light-emitting devices of Example 3, Comparative Example 4 andComparative Example 5 were investigated with respect to the chromaticitycoordinates of luminescent color. As a result, the chromaticitycoordinates were (0.33, 0.34) and Ra=86 in the case of Example 3, (0.35,0.36) and Ra=87 in the case of Comparative Example 4, and (0.38, 0.38)and Ra=78 in the case of Comparative Example 5. Namely, the emission ofwhite light was recognized in all of these examples.

However, with respect to the total luminous flux and emissionefficiency, while Example 4 indicated 65 (lm/W), Comparative Example 5indicated 20 (lm/W) and Comparative Example 5 indicated 58 (lm/W).

The light-emitting device of Example 3 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Examples. For the same reasons as explained in theaforementioned Example 1, due to the provision of thickness distributionin the yellow fluorescent layer 7, it becomes possible to absorb theexciting light without losing the exciting light, thus making itpossible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

EXAMPLE 4

In this example, a light-emitting device constructed as shown in FIG. 5was manufactured. By repeating the same procedures as described inExample 3, a transparent resin layer 5 and a red fluorescent layer 6were formed on the same kind of semiconductor light-emitting element 3as employed in Example 3.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 555 nm was dispersed in silicone resin to prepare a yellowfluorescent substance-dispersed resin. This yellow fluorescentsubstance-dispersed resin was laminated so as to entirely cover the redfluorescent layer 6 and to form a layer of an arch-like configurationhaving a uniform thickness, thereby forming a yellow fluorescent layer7. Then, a second transparent resin layer 11 was formed on the yellowfluorescent layer 7 in such a manner that the thickness “m” of the topportion thereof was made larger than the thickness “n” of each of endfaces thereof (i.e. m/n=2).

Further, a silicone resin layer containing a BCA green fluorescentsubstance exhibiting an emission peak at 480 nm was formed so as tocover the second transparent resin layer 11 and to have an arch-likeconfiguration having a uniform thickness, thereby forming a greenfluorescent layer 8 and obtaining the light-emitting device constructedas shown in FIG. 5.

COMPARATIVE EXAMPLE 6

The procedures described in Example 4 were repeated in the same mannerexcept that the second transparent resin layer 11 was coated uniformlyso as to create a thickness distribution wherein the ratio between thethickness “o” of the top portion thereof and the thickness “p” of eachof end face portions thereof became o/p=1, thereby manufacturing alight-emitting device having a construction as shown in FIG. 11.

The light-emitting devices of Example 4 and Comparative Example 6 wereinvestigated with respect to the chromaticity coordinates of luminescentcolor. As a result, the chromaticity coordinates were (0.35, 0.38) andRa=82 in the case of Example 4, and (0.38, 0.38) and Ra=78 in the caseof Comparative Example 6. Namely, the emission of white light wasrecognized in all of these examples.

However, with respect to the emission efficiency, while Example 4indicated 65 (lm/W), Comparative Example 6 indicated 61 (lm/W).

The light-emitting device of Example 4 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Example 6. For the same reasons as explained in theaforementioned Example 2, due to the provision of thickness distributionin the second transparent resin layer 11, it becomes possible to absorbthe exciting light without losing the exciting light, thus making itpossible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

EXAMPLE 5

In this example, a light-emitting device constructed as shown in FIG. 2was manufactured.

A near-ultraviolet semiconductor light-emitting element exhibiting anemission peak at a wavelength ranging from 400 to 410 nm and havingsuitable p/n electrodes was prepared as a semiconductor light-emittingelement 3, wherein the light-emitting element was provided with aGaN-based vertical resonator, with a reflecting mirror constituted by anSiO₂/ZrO₂ dielectric multi-layer film, and with a light-emitting layerconstituted by an AlGaN/GaN multiple quantum well active layer. Thissemiconductor light-emitting element 3 was then secured to the AlNsubstrate of package portion 1 using Au—Sn paste. The lead-out electrode2 a of the anode side was electrically connected with the p-typeelectrode of the LED chip by an Au wire 4. The lead-out electrode 2 b ofthe cathode side was electrically connected with the n-type electrode ofthe LED chip by Au—Sn paste.

Using a silicone-based transparent resin, a transparent resin layer 5was formed on the semiconductor light-emitting element 3. Specifically,first of all, while heating a substrate at a temperature of 150° C. inan air atmosphere and at atmospheric pressure and using a dispenser, asilicone-based transparent resin was coated on the substrate so as toform a layer of an arch-like configuration where a ratio between thethickness of the top portion thereof and the thickness of each of endface portions was approximately 1:1. Thereafter, the resultant body wasallowed to dry at atmospheric pressure at a temperature of 150° C. for10 to 90 minutes to obtain a transparent resin layer 5.

A CASN red fluorescent substance exhibiting an emission peak at awavelength of 655 nm was dispersed in silicone resin employed as abinder resin to prepare a red fluorescent substance-dispersed resin.While heating the substrate at a temperature of 150° C. in an airatmosphere and at atmospheric pressure and using a dispenser, the redfluorescent substance-dispersed resin was coated so as to entirely coverthe transparent resin layer 5 and to form a layer of an arch-likeconfiguration having a uniform thickness. Thereafter, the resultant bodywas allowed to dry at atmospheric pressure at a temperature of 150° C.for 10 to 90 minutes to obtain a red fluorescent layer 6. In this redfluorescent layer 6, a ratio between the thickness of the top portionthereof and the thickness of each of end face portions was approximately1:1.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 555 nm was dispersed in silicone transparent resin toprepare a yellow fluorescent substance-dispersed resin. While heatingthe substrate at a temperature of 150° C. in an air atmosphere and atatmospheric pressure, the yellow fluorescent substance-dispersed resinwas coated on the red fluorescent layer 6 so as to form a layer of anarch-like configuration where the thickness “a” of the top portionthereof was made larger than the thickness “b” of each of end faces(i.e. a/b=2). Thereafter, the resultant body was allowed to dry atatmospheric pressure at a temperature of 150° C. for 10 to 90 minutes toobtain a yellow fluorescent layer 7.

A BCA green fluorescent substance exhibiting an emission peak at awavelength of 480 nm was dispersed in silicone resin to prepare a greenfluorescent substance-dispersed resin. A BAM blue fluorescent substanceexhibiting an emission peak at a wavelength of 450 nm was dispersed insilicone resin to prepare a blue fluorescent substance-dispersed resin.While heating the substrate at a temperature of 150° C. and using adispenser, the green fluorescent substance-dispersed resin and the bluefluorescent substance-dispersed resin were successively coated on theyellow fluorescent layer 7 so as to entirely cover the underlyingfluorescent layer and to form a layer having an arch-like configurationhaving a uniform thickness.

Thereafter, the resultant body was allowed to dry at atmosphericpressure at a temperature of 150° C. for 10 to 90 minutes to cure all ofthese fluorescent layers to obtain a light-emitting device having aconstruction as shown in FIG. 2. In these green fluorescent layer 8 andblue fluorescent layer 9, a ratio between the thickness of the topportion thereof and the thickness of each of end face portions wasapproximately 1:1.

COMPARATIVE EXAMPLE 7

The same kinds of CASN red fluorescent substance, SOSE yellowfluorescent substance, BCA green fluorescent substance and BAM bluefluorescent substance as employed in Example 5 were prepared. Then, allof these four kinds of fluorescent substances were mixed with anddispersed in silicone resin to prepare a mixed fluorescentsubstance-dispersed resin.

A light-emitting device having a construction as shown in FIG. 6 wasprepared in the same manner as described above except that the mixedfluorescent substance-dispersed resin was coated on the transparentresin layer 5 to form a mixed fluorescent layer 10 having an arch-likeconfiguration. Incidentally, in this mixed fluorescent layer 10, a ratiobetween the thickness of the top portion thereof and the thickness ofeach of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 8

The procedures described in Example 5 were repeated in the same mannerexcept that the yellow fluorescent layer 7 was coated uniformly so thatthe ratio between the thickness “c” of the top portion thereof and thethickness “d” of each of end face portions thereof became 1:1 (i.e.c/d=1), thereby manufacturing a light-emitting device having aconstruction as shown in FIG. 7.

The light-emitting devices of Example 5, Comparative Example 7 andComparative Example 8 were investigated with respect to the chromaticitycoordinates of luminescent color. As a result, the chromaticitycoordinates were (0.34, 0.37) in the case of Example 5, (0.36, 0.36) inthe case of Comparative Example 7, and (0.38, 0.38) in the case ofComparative Example 8.

However, with respect to the total luminous flux and emissionefficiency, while Example 5 indicated 28.5 (lm/W) and Ra (colorrendering)=82; Comparative Example 7 indicated 9.5 (lm/W) and Ra=88. InComparative Example 8, they were 25.5 (lm/W) and Ra=88.

The light-emitting device of Example 4 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Examples. In the case of the light-emitting element chipemployed in Example 4, the light distribution characteristics thereofwere designed such that they were made higher in the vertical directionand made lower in the lateral direction. Therefore, for the same reasonsas explained in the above-described Example 1, due to the provision ofthickness distribution in the yellow fluorescent layer 7, it becomespossible to absorb the exciting light without losing the exciting light,thus making it possible to obtain a white light source which is high inemission efficiency and almost free from discoloration.

EXAMPLE 6

In this example, a light-emitting device constructed as shown in FIG. 3was manufactured.

By repeating the same procedures as described in Example 5, atransparent resin layer 5 and a red fluorescent layer 6 were formed onthe same kind of semiconductor light-emitting element 3 as employed inExample 5.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 552 nm was dispersed in silicone resin to prepare a yellowfluorescent substance-dispersed resin. This yellow fluorescentsubstance-dispersed resin was laminated so as to entirely cover the redfluorescent layer 6 and to form a layer of an arch-like configurationhaving a uniform thickness, thereby forming a yellow fluorescent layer7. Then, a second transparent resin layer 11 was formed on the yellowfluorescent layer 7 in such a manner that the thickness “e” of the topportion thereof was made larger than the thickness “f” of each of endfaces thereof (i.e. e/f=2).

Further, a silicone resin layer containing a BCA green fluorescentsubstance exhibiting an emission peak at 480 nm and a silicone resinlayer containing a BAM blue fluorescent substance exhibiting an emissionpeak at 450 nm were successively laminated so as to cover the secondtransparent resin layer 11, each layer having an arch-like configurationhaving a uniform thickness, thereby forming a green fluorescent layer 8and a blue fluorescent layer 9, respectively, thus obtaining thelight-emitting device constructed as shown in FIG. 3.

COMPARATIVE EXAMPLE 9

The procedures described in Example 6 were repeated in the same mannerexcept that the second transparent resin layer 11 was coated uniformlyso as to create a thickness distribution wherein the ratio between thethickness “g” of the top portion thereof and the thickness “h” of eachof end face portions thereof became g/h=1, thereby manufacturing alight-emitting device having a construction as shown in FIG. 8.

The light-emitting devices of Example 6 and Comparative Example 9 wereinvestigated with respect to the chromaticity coordinates of luminescentcolor. As a result, the chromaticity coordinates were (0.35, 0.38) andRa=87 in the case of Example 6, and (0.38, 0.38) and Ra=88 in the caseof Comparative Example 9. Namely, the emission of white light wasrecognized in all of these examples.

However, with respect to the emission efficiency, while Example 6indicated 27 (lm/W), Comparative Example 9 indicated 25 (lm/W).

The light-emitting device of Example 6 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Example 9. For the same reasons as explained in theaforementioned Example 2, due to the provision of thickness distributionin the second transparent resin layer 11, it becomes possible to absorbthe exciting light without losing the exciting light, thus making itpossible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

EXAMPLE 7

In this example, a light-emitting device constructed as shown in FIG. 4was manufactured.

A blue semiconductor light-emitting element exhibiting an emission peakat a wavelength ranging from 450 to 460 nm and having suitable p/nelectrodes was prepared as a semiconductor light-emitting element 3,wherein the light-emitting element was provided with a GaN-basedvertical resonator, with a reflecting mirror constituted by an SiO₂/ZrO₂dielectric multi-layer film, and with a light-emitting layer constitutedby an InGaN/InGaN multiple quantum well active layer. This semiconductorlight-emitting element 3 was then secured to the AlN substrate ofpackage portion 1 using an Au—Sn paste. The lead-out electrode 2 a ofthe anode side was electrically connected with the p-type electrode ofthe LED chip by an Au wire 4. The lead-out electrode 2 b of the cathodeside was electrically connected with the n-type electrode of the LEDchip by Au—Sn paste.

Using a silicone-based transparent resin, a transparent resin layer 5was formed on the semiconductor light-emitting element 3. Specifically,first of all, while heating a substrate at a temperature of 150° C. inan air atmosphere and at atmospheric pressure and using a dispenser, asilicone-based transparent resin was coated on the substrate so as toform a layer of an arch-like configuration where a ratio between thethickness of the top portion thereof and the thickness of each of endface portions was approximately 1:1. Thereafter, the resultant body wasallowed to dry at atmospheric pressure at a temperature of 150° C. for10 to 90 minutes to obtain a transparent resin layer 5.

A CASN red fluorescent substance exhibiting an emission peak at awavelength of 655 nm was dispersed in silicone resin employed as abinder resin to prepare a red fluorescent substance-dispersed resin.While heating the substrate at a temperature of 150° C. in an airatmosphere and at atmospheric pressure and using a dispenser, the redfluorescent substance-dispersed resin was coated so as to entirely coverthe transparent resin layer 5 and to form a layer of an arch-likeconfiguration having a uniform thickness. Thereafter, the resultant bodywas allowed to dry at atmospheric pressure at a temperature of 150° C.for 10 to 90 minutes to obtain a red fluorescent layer 6. In this redfluorescent layer 6, a ratio between the thickness of the top portionthereof and the thickness of each of end face portions was approximately1:1.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 555 nm was dispersed in silicone transparent resin toprepare a yellow fluorescent substance-dispersed resin. While heatingthe substrate at a temperature of 150° C. in an air atmosphere and atatmospheric pressure, the yellow fluorescent substance-dispersed resinwas coated on the red fluorescent layer 6 so as to form a layer of anarch-like configuration where the thickness “i” of the top portionthereof was made larger than the thickness “j” of each of end faces(i.e. i/j=1.5). Thereafter, the resultant body was allowed to dry atatmospheric pressure at a temperature of 150° C. for 10 to 90 minutes toobtain a yellow fluorescent layer 7.

A BCA green fluorescent substance exhibiting an emission peak at awavelength of 480 nm was dispersed in silicone resin to prepare a greenfluorescent substance-dispersed resin. While heating the substrate at atemperature of 150° C. and using a dispenser, the green fluorescentsubstance-dispersed resin was coated on the yellow fluorescent layer 7so as to entirely cover the yellow fluorescent layer 7 and to form alayer having an arch-like configuration having a uniform thickness.

Thereafter, the resultant body was allowed to dry at atmosphericpressure at a temperature of 150° C. for 10 to 90 minutes to cure all ofthese fluorescent layers to obtain a light-emitting device having aconstruction as shown in FIG. 4. In the green fluorescent layer 8, aratio between the thickness of the top portion thereof and the thicknessof each of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 10

The same kinds of CASN red fluorescent substance, SOSE yellowfluorescent substance and BCA green fluorescent substance as employed inExample 7 were prepared. Then, all of these three kinds of fluorescentsubstances were mixed with and dispersed in silicone resin to prepare amixed fluorescent substance-dispersed resin.

A light-emitting device having a construction as shown in FIG. 9 wasprepared in the same manner as described above except that the mixedfluorescent substance-dispersed resin was coated on the transparentresin layer 5 to form a mixed fluorescent layer 10 having an arch-likeconfiguration. Incidentally, in this mixed fluorescent layer 10, a ratiobetween the thickness of the top portion thereof and the thickness ofeach of end face portions was approximately 1:1.

COMPARATIVE EXAMPLE 11

The procedures described in Example 7 were repeated in the same mannerexcept that the yellow fluorescent layer 7 was coated uniformly so thatthe ratio between the thickness “k” of the top portion thereof and thethickness “l” of each of end face portions thereof became 1:1 (i.e.k/l=1), thereby manufacturing a light-emitting device having aconstruction as shown in FIG. 10.

The light-emitting devices of Example 7, Comparative Example 10 andComparative Example 11 were investigated with respect to thechromaticity coordinates of luminescent color. As a result, thechromaticity coordinates were (0.33, 0.34) and Ra=86 in the case ofExample 7, (0.35, 0.36) and Ra=87 in the case of Comparative Example 10,and (0.38, 0.38) and Ra=78 in the case of Comparative Example 11.Namely, the emission of white light was recognized in all of theseexamples.

However, with respect to the total luminous flux and emissionefficiency, while Example 7 indicated 33 (lm/W), Comparative Example 10indicated 10 (lm/W) and Comparative Example 11 indicated 29 (lm/W).

The light-emitting device of Example 7 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Examples. For the same reasons as explained in theabove-described Example 1, due to the provision of thicknessdistribution in the yellow fluorescent layer 7, it becomes possible toabsorb the exciting light without losing the exciting light, thus makingit possible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

EXAMPLE 8

In this example, a light-emitting device constructed as shown in FIG. 5was manufactured. By repeating the same procedures as described inExample 7, a transparent resin layer 5 and a red fluorescent layer 6were formed on the same kind of semiconductor light-emitting element 3as employed in Example 7.

An SOSE yellow fluorescent substance exhibiting an emission peak at awavelength of 555 nm was dispersed in silicone resin to prepare a yellowfluorescent substance-dispersed resin. This yellow fluorescentsubstance-dispersed resin was laminated so as to entirely cover the redfluorescent layer 6 and to form a layer of an arch-like configurationhaving a uniform thickness, thereby forming a yellow fluorescent layer7. Then, a second transparent resin layer 11 was formed on the yellowfluorescent layer 7 in such a manner that the thickness “m” of the topportion thereof was made larger than the thickness “n” of each of endfaces thereof (i.e. m/n=2).

Further, a silicone resin layer containing a BCA green fluorescentsubstance exhibiting an emission peak at 480 nm was laminated so as tocover the second transparent resin layer 11, thereby forming a greenfluorescent layer 8 having a uniform thickness and an arch-likeconfiguration, thus obtaining the light-emitting device constructed asshown in FIG. 5.

COMPARATIVE EXAMPLE 12

The procedures described in Example 8 were repeated in the same mannerexcept that the second transparent resin layer 11 was coated uniformlyso as to create a thickness distribution wherein the ratio between thethickness “o” of the top portion thereof and the thickness “p” of eachof end face portions thereof became o/p=1, thereby manufacturing alight-emitting device having a construction as shown in FIG. 11.

The light-emitting devices of Example 8 and Comparative Example 12 wereinvestigated with respect to the chromaticity coordinates of luminescentcolor. As a result, the chromaticity coordinates were (0.35, 0.38) andRa=82 in the case of Example 8, and (0.38, 0.38) and Ra=78 in the caseof Comparative Example 12. Namely, the emission of white light wasrecognized in all of these examples.

However, with respect to the emission efficiency, while Example 8indicated 33 (lm/W), Comparative Example 12 indicated 31 (lm/W).

The light-emitting device of Example 8 was found more improved inemission efficiency as compared with the light-emitting device ofComparative Example 12. For the same reasons as explained in theaforementioned Example 2, due to the provision of thickness distributionin the second transparent resin layer 11, it becomes possible to absorbthe exciting light without losing the exciting light, thus making itpossible to obtain a white light source which is high in emissionefficiency and almost free from discoloration.

According to the embodiment of the present invention, it is possible toprovide a light-emitting device which is capable of realizing a whitelight source exhibiting a high emission efficiency.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A light-emitting device comprising: a package having, on a surfacethereof, a first portion and a second portion surrounding the firstportion; a semiconductor light-emitting element mounted on the firstportion and emitting a light having an emission peak at anear-ultraviolet region; a transparent resin layer covering thesemiconductor light-emitting element and contacted with the firstportion and the second portion, the transparent resin layer having anarch-like outer profile, as seen in a cross section when cutperpendicularly to the surface; and a laminated body formed on thetransparent resin layer with end faces of the laminated body beingcontacted with the second portion, the laminated body having anarch-like outer profile, as seen in a cross section when cutperpendicularly to the surface and comprising a red fluorescent layer, ayellow fluorescent layer, a green fluorescent layer and a bluefluorescent layer which are laminated in the mentioned order, the yellowfluorescent layer having a top portion larger in thickness than that ofthe end face portions thereof.
 2. The device according to claim 1,wherein in the yellow fluorescent layer, a thickness of the top portionis at least 1.5 times larger than that of the end faces.
 3. The deviceaccording to claim 1, wherein in yellow fluorescent layer, a thicknessof the top portion is not more than four times larger than that of theend faces.
 4. The device according to claim 1, wherein in the yellowfluorescent layer, a thickness of the top portion thereof is twicelarger than that of the end faces.
 5. The device according to claim 1,wherein a wavelength of the light emitted from the semiconductorlight-emitting element is confined within the range of 375-420 nm.
 6. Alight-emitting device comprising: a package having, on a surfacethereof, a first portion and a second portion surrounding the firstportion; a semiconductor light-emitting element mounted on the firstportion and emitting a light having an emission peak at anear-ultraviolet region; a first transparent resin layer covering thesemiconductor light-emitting element and contacted with the firstportion and the second portion, the first transparent resin layer havingan arch-like outer profile, as seen in a cross section when cutperpendicularly to the surface; and a laminated body formed on the firsttransparent resin layer with end faces of the laminated body beingcontacted with the second portion, the laminated body having anarch-like outer profile, as seen in a cross section when cutperpendicularly to the surface and comprising a red fluorescent layer, ayellow fluorescent layer, a second transparent resin layer, a greenfluorescent layer and a blue fluorescent layer which are laminated inthe mentioned order, the second transparent resin layer having a topportion larger in thickness than that of the end face portions thereof.7. The device according to claim 6, wherein in the second transparentresin layer, a thickness of the top portion is at least 1.5 times largerthan that of the end faces.
 8. The device according to claim 6, whereinin the second transparent resin layer, a thickness of the top portion isnot more than four times larger than that of the end faces.
 9. Thedevice according to claim 6, wherein in the second transparent resinlayer, a thickness of the top portion is twice larger than that of theend faces.
 10. The device according to claim 6, wherein a wavelength ofthe light emitted from the semiconductor light-emitting element isconfined within the range of 375-420 nm.
 11. A light-emitting devicecomprising: a package having, on a surface thereof, a first portion anda second portion surrounding the first portion; a semiconductorlight-emitting element mounted on the first portion and emitting a lighthaving an emission peak at a blue color region; a transparent resinlayer covering the semiconductor light-emitting element and contactedwith the first portion and the second portion, the transparent resinlayer having an arch-like outer profile, as seen in a cross section whencut perpendicularly to the surface; and a laminated body formed on thetransparent resin layer with end faces of the laminated body beingcontacted with the second portion, the laminated body having anarch-like outer profile, as seen in a cross section when cutperpendicularly to the surface and comprising a red fluorescent layer, ayellow fluorescent layer and a green fluorescent layer which arelaminated in the mentioned order, the yellow fluorescent layer having atop portion made larger in thickness than that of the end face portionsthereof.
 12. The device according to claim 11, wherein in the yellowfluorescent layer, a thickness of the top portion is at least 1.5 timeslarger than that of the end faces thereof.
 13. The device according toclaim 11, wherein in the yellow fluorescent layer, a thickness of thetop portion is not more than four times larger than that of the endfaces.
 14. The device according to claim 11, wherein in the yellowfluorescent layer, a thickness of the top portion is twice larger thanthat of the end faces.
 15. The device according to claim 11, wherein awavelength of the light emitted from the semiconductor light-emittingelement is confined within the range of 430-480 nm.
 16. A light-emittingdevice comprising: a package having, on a surface thereof, a firstportion and a second portion surrounding the first portion; asemiconductor light-emitting element mounted on the first portion andemitting a light having an emission peak at a blue color region; a firsttransparent resin layer covering the semiconductor light-emittingelement and contacted with the first portion and the second portion, thefirst transparent resin layer having an arch-like outer profile, as seenin a cross section when cut perpendicularly to the surface; and alaminated body formed on the first transparent resin layer with endfaces of the laminated body being contacted with the second portion, thelaminated body having an arch-like outer profile, as seen in a crosssection when cut perpendicularly to the surface and comprising a redfluorescent layer, a yellow fluorescent layer, a second transparentresin layer and a green fluorescent layer which are laminated in thementioned order, the second transparent resin layer having a top portionmade larger in thickness than that of the end face portions thereof. 17.The device according to claim 16, wherein in the second transparentresin layer, a thickness of the top portion is at least 1.5 times largerthan that of the end faces.
 18. The device according to claim 16,wherein in the second transparent resin layer, a thickness of the topportion is not more than four times larger than that of the end faces.19. The device according to claim 16, wherein in the second transparentresin layer, a thickness of the top portion is twice larger than that ofthe end faces.
 20. The device according to claim 16, wherein awavelength of the light emitted from the semiconductor light-emittingelement is confined within the range of 430-480 nm.